Rounded Ends (or caps) on Biezer Curve Pipe
Make 2 bend curve as seen in the image.
Make a small circle curve.
In Object mode select the bend curve and go to curve tab at the right hand.
In the Geometry panel under Bevel Object select the circle.


As soon as you click the circle you will get the tube shape. If you scale the circle you will find the tube getting thicker and thicker.

If you want to fill the caps of the tube:

In the Geometry panel under the Bevel Factor choose Fill caps.
If you check on the caps the opening will be closed and if you uncheck it the opening will be open.